Super-junction trench mosfets with short terminations

ABSTRACT

A super-junction trench MOSFET with a short termination area is disclosed, wherein the short termination area comprising a charge balance region and a channel stop region formed near a top surface of an epitaxial layer with a trenched termination contact penetrating therethrough.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part (CIP) of U.S. patent application Ser. No. 13/751,458 of the same inventor, filed on Jan. 28, 2013, entitled “super-junction trench MOSFET having deep trenches with buried voids”.

FIELD OF THE INVENTION

This invention relates generally to the cell structure, device configuration and fabrication process of semiconductor power devices. More particularly, this invention relates to a novel and improved cell structure, device configuration and improved process of a super-junction trench metal oxide semiconductor field effect transistor (MOSFET, the same hereinafter).

BACKGROUND OF THE INVENTION

Compared with the conventional trench MOSFETs, super-junction trench MOSFETs are more attractive due to higher breakdown voltage and lower specific Rds (drain-source resistance). As shown in FIG. 1, U.S. patent application Ser. No. 13/751,458 of the same inventor as the present invention discloses a super-junction trench MOSFET 100 comprising a termination area including multiple guard rings (“GR”, as illustrated in FIG. 1), wherein the termination area is about 200 um in length due to the multiple guard rings. However, for the integration of semiconductor power devices is more and more advanced, a super-junction trench MOSFET with short termination is admired because it takes up less space and is more cost effective due to its smaller device size.

Therefore, there is still a need in the art of the semiconductor power device, particularly for super-junction trench MOSFET design and fabrication, to provide a novel cell structure, device configuration and fabrication process that would resolve these difficulties and design limitations.

SUMMARY OF THE INVENTION

The present invention provides a super-junction trench MOSFET having short termination about 20 um in length, shortening termination length to about one tenth compared with the prior art, which is more flexible in applications and more cost effective due to its smaller device size.

According to an aspect, the present invention features a super-junction trench MOSFET comprising a plurality of unit cells with each unit cell in an active area having a first type charge balance area consist of two P/N charge balance areas formed in the mesa area between adjacent deep trenches, comprising: a substrate of a first conductivity type; an epitaxial layer of the first conductivity type grown on the substrate, the epitaxial layer having a lower doping concentration than the substrate; a plurality of deep trenches filled with dielectric material, starting from a top surface of the epitaxial layer and down extending into the substrate, each comprising a void inside the dielectric material; a mesa between the pair of deep trenches; a first doped column region of the first conductivity type with column shape within each the mesa; a pair of second doped column regions of a second conductivity type with column shape adjacent to sidewalls of the pair of deep trenches within the mesa, in parallel with and surrounding the first doped column region forming a first type charge balance area in conjunction with the first doped column region; a body region of the second conductivity type in the mesa, covering a top surface of the first and second doped column regions, extending between the deep trenches; at least one gate trench filled with doped poly-silicon layer padded by a gate oxide layer, starting from the top surface of the epitaxial layer and down penetrating through the body region and extending into the first doped column in the mesa; multiple trenched source-body contacts with each filled with a contact metal plug extending into the body region in the mesa; a source region of the first conductivity type surrounding an upper portion of each the gate trench, extending between the upper portion of each the gate trench and sidewalls of adjacent trenched source-body contacts; and a termination area comprising a second type P/N charge balance area and a channel stop region formed near the top surface of the epitaxial layer with a doping concentration higher than the epitaxial layer.

According to another aspect of the present invention, in some preferred embodiments, the third doped column region in the termination area has about half column width of the first doped column region and the fourth doped column region has about same column width as the second doped column region in the unit cells.

According to another aspect of the present invention, in some preferred embodiments, the channel stop region has a trenched termination contact filled with the contact metal plug penetrating through the channel stop region.

According to another aspect of the present invention, in some preferred embodiments, the super-junction trench MOSFET further comprises a body contact region of the second conductivity type surrounding at least bottom of each of the multiple trenched source-body contacts, wherein the body contact region has a higher doping concentration than the body region.

According to another aspect of the present invention, in some preferred embodiments, the super-junction trench MOSFET further comprises a body contact region of the second conductivity type surrounding at least bottom of the trenched termination contact, wherein the body contact region has a higher doping concentration than the body region.

According to another aspect of the present invention, in some preferred embodiments, the contact metal plug is a tungsten plug padded by a barrier metal layer of Ti/TiN or Co/TiN or Ta/TiN.

According to another aspect of the present invention, in some preferred embodiments, the super-junction trench MOSFET further comprises an equal potential ring metal covering the contact metal plug filled in the trenched termination contact in the termination area and a passivation layer covering a top surface of the termination area.

According to another aspect of the present invention, in some preferred embodiments, the void inside the deep trench in the termination area is not opened up in air.

According to another aspect of the present invention, in some preferred embodiments, the void inside the deep trench in the termination area is opened up in air. And in some preferred embodiments, the super-junction trench MOSFET further comprises a passivation layer covering above the void inside the deep trench in the termination area.

The present invention also features a method for manufacturing a super-junction trench MOSFET comprising the steps of: forming a plurality of deep trenches in active area inside an epitaxial layer of a first conductivity type onto a substrate of the first conductivity type; carrying out angle ion implantations of the first conductivity type dopant and diffusion through the deep trenches to form a first doped column region of the first conductivity type with column shape within a mesa area between every two adjacent of the deep trenches; carrying out angle ion implantations of a second conductivity type dopant and diffusion through the deep trenches to form second doped column regions of the second conductivity type with column shape adjacent to sidewalls of the deep trenches, in parallel with and surrounding the first doped column region; forming a third doped column of the first conductivity type and a fourth doped column of the second conductivity through a deep trench in termination area simultaneously with the first doped column and the second doped column within the mesa, respectively; depositing a dielectric material with voids in the deep trenches; removing the dielectric material from top surface of the epitaxial layer; forming a pad oxide layer prior to forming body regions; forming a channel stop region near the top surface of the epitaxial layer in the termination area and source regions in the active area at same step by carrying out source ion implantation; depositing a contact interlayer on the top surface of the epitaxial layer; forming a trenched termination contact penetrating through the channel stop region into the epitaxial layer in the termination area and multiple trenched source-body contacts in the active area by doing successively dry oxide etch and dry silicon etch; and depositing a tungsten layer padded with a barrier metal layer and then etching back to form contact metal plugs respectively filled in the trenched termination contact and the multiple trenched source-body contacts.

These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a super-junction trench MOSFET of U.S. patent application Ser. No. 13/751,458 of the same inventor.

FIG. 2A is a cross-sectional view of a preferred embodiment according to the present invention.

FIG. 2B is a cross-sectional view of another preferred embodiment according to the present invention.

FIG. 2C is a cross-sectional view of another preferred embodiment according to the present invention.

FIG. 3A is a cross-sectional view of another preferred embodiment according to the present invention.

FIG. 3B is a cross-sectional view of another preferred embodiment according to the present invention.

FIGS. 4A-4K are a serial of cross-sectional views for showing the processing steps for fabricating the super-junction trench MOSFET according to the present invention.

FIGS. 5A and 5B are cross-sectional views for showing the processing steps for forming the opened up void of another super-junction trench MOSFET according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following Detailed Description, reference is made to the accompanying drawings, which forms a part thereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top”, “bottom”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purpose of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be make without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise.

Please refer to FIG. 2A for a preferred embodiment of this invention wherein an N-channel super-junction trench MOSFET 200 is formed in an N− epitaxial layer 201 supported onto an N+ substrate 202 which coated with a back metal 203 of Ti/Ni/Ag on its rear side as drain metal. The N-channel super-junction trench MOSFET 200 comprises a plurality of unit cells with each comprising a plurality of deep trenches 204 formed starting form a top surface of the N− epitaxial layer 201 and vertically down extending into the INT+ substrate 202. Inside each of the deep trenches 204, a thick dielectric layer 205 with a buried void is formed therein. A mesa is therefore formed between every two adjacent of the deep trenches 204 in each unit cell wherein an N first doped column region 206 consist of two N sub-doped column regions 206′ each having half column width of the N first doped column region 206 is formed. Adjacent to sidewalls of the deep trenches 204, a pair of P second doped column regions 207 is formed in the mesa and in parallel surrounding with the N first doped column region 206. A first type charge balance area comprising two P/N charge balance areas is formed in the mesa area between the adjacent deep trenches. The N first doped column region 206 and the P second doped column regions 207 all have column bottoms above trench bottoms of the deep trenches 204. Onto a top surface of the N first doped column region 206 and the P second doped column regions 207, a p body region 208 is formed between in the mesa extending between every two adjacent of the deep trenches 204. A pair of gate trenches 209 are penetrating through the p body region 208 further extending into the N first doped column region 206 in each unit cell, wherein the pair of gate trenches 209 each comprises a gate electrode 210 padded by a gate oxide layer 211. In some preferred embodiments, there is only one gate trench penetrating through the p body region further extending into the N first doped column region in each unit cell as an alternative. Onto a top surface of the gate electrodes 210, the contact interlayer 212 is formed to isolate the gate electrodes 210 from the source metal 213. In each the mesa, multiple trenched source-body contacts 214 with each filled with a tungsten plug 215 are formed penetrating through the contact interlayer 212 and extending into the p body region 208 in each unit cell, and an n+ source regions 216 is formed surrounding an upper portion of the gate trenches 209, extending between the upper portion of the gate trenches 209 and sidewalls of adjacent trenched source-body contacts 214. Therefore, the p body region 208 and the n+ source region 216 are connected to the source metal 213 via the multiple trenched source-body contacts 214. Furthermore, a p+ body contact region 221 is formed surrounding at least bottom of each the trenched source-body contact 214 to reduce the contact resistance between the tungsten plugs 215 and the p body region 208. As shown in dashed brace, each the P second doped column region 207 and the adjacent N sub-doped column region 206′ constitute the P/N charge balance area. In the termination area, a N third doped column region 236 and a P fourth doped column region 237 near a deep trench 234 filled with the thick dielectric layer 205 having a void 230, constitute a second type charge balance area, wherein the N third doped column region 236 has about half column width of the N first doped column region 206 and the fourth doped column region 237 has about same column width as the second doped column region 236 in the unit cell. Therefore, there is no need to have multiple guard rings in the termination area as in the prior art. Moreover, top surface of the void 230 in FIG. 2A is sealed with the thick dielectric layer 205. Besides, an n+ channel stop region 222 is formed near the top surface of the N− epitaxial layer 201 with a trenched termination contact 223 penetrating through the contact interlayer 212, the n+ channel stop region 222 and into the N− epitaxial layer 201, wherein the trenched termination contact 223 has a same filling material with the trenched source-body contact 214 and is connected to an equal potential ring (EPR, the same hereinafter) metal 224, A p+ body contact region 221′ is formed surrounding at least bottom of the trenched termination contact 223 to reduce the contact resistance. In this preferred embodiment, all the contact metal plugs can be implemented by using a tungsten plug padded by a barrier metal layer of Ti/TiN or Co/TiN or Ta/TiN. Therefore, the termination area according to the present invention is about 20 um in length, shortening termination length to about one tenth compared with the prior art.

FIG. 2B shows a cross-sectional view of another preferred super-junction trench MOSFET 200′ according to the present invention which has a similar structure as the super-junction trench MOSFET 200 in FIG. 2A except that in FIG. 2B, there is no EPR metal connected with the trenched termination contact 223′ in the termination area.

FIG. 2C shows a cross-sectional view of another preferred super-junction trench MOSFET 200″ according to the present invention which has a similar structure as the super-junction trench MOSFET 200 in FIG. 2A except that in FIG. 2C, the super-junction trench MOSFET 200″ further comprises a passivation layer 260 covering a whole top surface of the termination area including a portion of a top surface of source metal 213″ near the termination area.

FIG. 3A shows a cross-sectional view of another preferred super-junction trench MOSFET 300 according to the present invention which has a similar structure as the super-junction trench MOSFET 200 in FIG. 2A except that in FIG. 3A, the void inside the deep trench 334 in the termination area is opened up in air. Moreover, the EPR metal extends from the channel stop area toward active area and stop before the void.

FIG. 3B shows a cross-sectional view of another preferred super-junction trench MOSFET 300′ according to the present invention which has a similar structure as the super-junction trench MOSFET 300 in FIG. 3A except that in FIG. 3B, the super-junction trench MOSFET 300′ further comprises a passivation layer 360 covering above the void inside the deep trench 334′ in the termination area.

FIGS. 4A to 4K are a serial of exemplary steps that are performed to form the inventive super-junction trench MOSFET 200 in FIG. 2A. In FIG. 4A, an N− epitaxial layer 201 is grown on an N+ substrate 202, wherein the N+ substrate 202 has a higher doping concentration than the N− epitaxial layer 201, and shares a common interface with the N− epitaxial layer 201, Next, a hard mask 270, which can be implemented by using an oxide layer, is formed covering a top surface of the N− epitaxial layer 201. Then, after a trench mask (not shown) is applied onto the hard mask 270, deep trenches 204′ and 234′ is etched through the hard mask 270 and into the N− epitaxial layer 201 by successively dry oxide etch and dry silicon etch.

In FIG. 4B, an isotropic dry silicon etch in down stream plasma is carried out to eliminate the plasma damage introduced during opening the deep trenches 204′ and 234′ and to form the deep trenches 204 and 234. The hard mask 270 is still remained to block sequential angle ion implantations into the top surface of the N− epitaxial layer 201.

In FIG. 4C, a pad oxide 271 of about 100 angstroms in thickness is grown along inner surfaces of the deep trenches 204 and 234. Then, an angle ion implantation of Phosphorus dopant followed by a Phosphorus dopant drive-in step is carried out to form an N first doped column region 206 consist of two N sub-doped column regions 206′ in a mesa between sidewalls of the deep trenches 204 and 234.

In FIG. 4D, another angle ion implantation of Boron dopant is carried out and followed by a Boron dopant drive-in step to form a pair of P second doped column regions 207 with column shape adjacent to the sidewalls of the deep trenches 204 and 234, in parallel with and surrounding the N first doped column region 206.

In termination areas of FIGS. 4C and 4D, an N third doped column 236 and a P fourth doped column 237 is simultaneously formed with the N first doped column 206 and the P second doped column, respectively.

In FIG. 4E, the hard mask 270 (as shown in FIG. 4D) and the pad oxide 271 (as shown in FIG. 4D) are removed away. A dielectric material 205, for example tetra ethyl ortho silicate (TEOS, the same hereinafter) is formed filling the deep trenches 204 and 234 with a buried void inside the dielectric material 205 and followed by an annealing process. Then, etching back or chemical mechanical polishing (CMP, the same hereinafter) the dielectric material 205 from the top surface of the N− epitaxial layer 201.

In FIG. 4F, a pad oxide layer 273 is formed on a top surface of the whole device structure in FIG. 4E. Then by applying a p body mask 274, p body ion implantation and diffusion are successively carried out to form a p body region 208 extending between the deep trenches 204 and 234 and near the top surface of the N− epitaxial layer 201. After that, the p body mask 274 is removed.

In FIG. 4G, after applying a gate trench mask (not shown), a plurality of gate trenches 209 are etched into the N first doped column region 206. Afterwards, a sacrificial oxide (not shown) is grown and then removed to eliminate the plasma damage introduced during opening the gate trenches 209.

In FIG. 4H, a gate oxide layer 211 is grown along inner surfaces of the gate trenches 209. Then, a doped poly-silicon layer is deposited to fill the gate trenches 209, and then is etched back by CMP or plasma etch to serve as gate electrodes 210.

In FIG. 4I, by applying a source mask 277, an ion implantation of n type dopant and a diffusion step are carried out to form n+ source regions 216 near a top surface of the p body region 208 in active area, and an n+ channel stop region 222 near the top surface of the N− epitaxial layer 201 in termination area.

In FIG. 4J, an insulation layer is deposited onto a whole top surface of the device structure to serve as a contact interlayer 212. Then, after applying a contact mask (not shown) onto the contact interlayer 212, a plurality of contact holes 278 and 278′ are formed by successively dry oxide etch and dry silicon etch. After penetrating through the contact interlayer 212, the contact holes 278 are further penetrating through the n+ source regions 216 and extending into the p body region 208 in the mesa, the contact hole 278′ is extending into the N− epitaxial layer 201. Next, a BF2 ion implantation is performed and followed by a step of RTA (rapid thermal annealing) process to form a plurality of p+ body contact regions 221 and p+ body contact region 221′ respectively surrounding at least bottoms of the contact holes 278 and 278′.

In FIG. 4K, a barrier metal layer Ti/TiN or Co/TiN or Ta/TiN is deposited on sidewalls and bottoms of all the contact holes. Then, a tungsten material layer is deposited onto the barrier metal layer, wherein the tungsten material layer and the barrier metal layer are then etched back to form: contact metal plugs 215 for trenched source-body contacts 214 and contact metal plug 215′ for trenched termination contact 223. Then, a metal layer of Al alloys or Cu padded by a resistance-reduction layer Ti or Ti/TiN underneath is deposited onto the contact interlayer 212 and followed by a metal etching process by employing a metal mask (not shown) to form a source metal 213 and an EPR metal 224.

FIGS. 5A and 5B show processing steps for forming the opened up void of the inventive super-junction trench MOSFET 300 in FIG. 3A. After formation of trenched source-body contacts 314 and trenched termination contact 323, a metal layer of Al alloys or Cu padded by a resistance-reduction layer Ti or Ti/TiN underneath is deposited onto the contact interlayer 312 and followed by a metal etching process by employing a metal mask (not shown) to form a source metal 313 and an EPR metal 324. Then in FIG. 5B, a dry oxide etch is performed to open up the void inside the deep trench 334 in the termination area by removing oxide in an upper portion of the deep trench 334.

Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention. 

What is claimed is:
 1. A method for manufacturing a super junction trench MOSFET comprising the steps of: forming a plurality of deep trenches in active area inside an epitaxial layer of a first conductivity type onto a substrate of said first conductivity type; carrying out angle ion implantations of said first conductivity type dopant and diffusion through said deep trenches to form a first doped column region of said first conductivity type with column shape within a mesa area between every two adjacent of said deep trenches; carrying out angle ion implantations of a second conductivity type dopant and diffusion through said deep trenches to form second doped column regions of said second conductivity type with column shape adjacent to sidewalls of said deep trenches, in parallel with and surrounding said first doped column region; forming a third doped column of said first conductivity type and a fourth doped column of said second conductivity through a deep trench in termination area simultaneously with said first doped column and said second doped column within said mesa, respectively; depositing a dielectric material with voids in said deep trenches; removing said dielectric material from top surface of said epitaxial layer; forming a pad oxide layer prior to forming body regions; and forming a channel stop region near the top surface of said epitaxial layer in said termination area and source regions in said active area at same step by carrying out source ion implantation.
 2. The method of claim 1 further comprising the steps of: depositing a contact interlayer on the top surface of said epitaxial layer; forming a trenched termination contact penetrating through said channel stop region into said epitaxial layer in said termination area and multiple trenched source-body contacts in said active area by doing successively dry oxide etch and dry silicon etch; and depositing a tungsten layer padded with a barrier metal layer, and then etching back to form contact metal plugs respectively filled in said trenched termination contact and said multiple trenched source-body contacts.
 3. The method of claim 2 further comprising forming a body contact region of said second conductivity type surrounding at least bottom of each of said multiple trenched source-body contacts and said trenched termination contact by carrying out an ion implantation of said second conductivity prior to depositing said tungsten layer.
 4. The method of claim 1 further comprising removing said dielectric material in an upper portion of said deep trench in said termination area to open up said void. 